Automakers are pushing back against an Obama administration proposal that would almost double vehicle fuel-efficiency standards, launching a new ad campaign warning of hundreds of thousands of job losses across the country.

The White House has long been negotiating with automakers and environmentalists over the enormous increase in fuel efficiency standards. But the automakers, who say the standards would stagger the auto industry, appear to be losing faith in the possibility of a compromise.

President Obama was hoping to get automakers to sign off on a nearly 100 percent increase in mileage standards by 2025, aiming for another Rose Garden announcement like the one in May 2009 when he announced they would raise it to 29.5 miles-per-gallon for model year 2012, on their way to 34 miles-per-gallon for 2016.